1. Field of the Invention
The present invention relates to a motor provided with a brush.
2. Description of the Related Art
In a motor provided with a brush, the brush is worn and shortened due to electrical sparking generated between the brush and segments. It is possible to improve a life span of the motor by reducing the wear of the brush caused by sparking. As a method for reducing the wear of the brush caused by sparking, the number of segments in a commutator being increased by two times the number of teeth has been disclosed in Japanese Patent Application publication No. 2008-113485, for example. Particularly, since a space factor is high in the case of a motor with a concentrated winding, electrical energy accumulated in a coil is increased. Therefore, it is important to reduce the wear due to sparking.
The motor disclosed in Japanese Patent Application publication No. 2008-113485 has a small potential difference between the segments, upon comparison with the case where the number of segments is the same with the number of teeth. Therefore, the sparks are reduced. If the number of segments is the same with the number of teeth, a border between the segments is placed so as to be matched with a position of teeth. If the number of segments is twice the number of teeth, a border between the segments is also positioned between the teeth. In the motor of the related art where the number of segments is twice the number of teeth, a first coil wound in a forward direction and a second coil wound in a reverse direction are disposed in each of the teeth. Therefore, when the brush is in contact with the new segment positioned between the teeth, electrification with respect to the coil on the tooth disposed at a position deviated at 180° in electric angles is switched. As a result, even in the case where the number of segments is twice the number of teeth, it is possible to produce the same torque as in the case where the number of segments is the same as the number of teeth.
However, in the winding structure described above, it is necessary to wind a coil in the forward direction and the reverse direction on a tooth, and thus the winding process and the leading-out of a conducting wire to the segment become complicated. Therefore, a number of man-hours required to make the motor is increased.